The present invention relates generally to roof ventilating devices, and methods of constructing and utilizing them in typical flat, or near flat roofs, of the type used mainly for commercial and industrial buildings.
Such roofs consist of a structural roof deck, normally covered by a vapor barrier on top of which is insulation and an impermeable synthetic plastic roofing membrane of the type disclosed, for instance, in the present assignee's U.S. Pat. No. 4,652,321, wherein the membrane consists of a woven polyester core fabric encased in a thermoplastic, synthetic plastic sheath, which typically may be polyvinyl chloride. With insulation sandwiched between the vapor barrier membrane and the outer roof surface membrane, a water and vapor trap may be created which tends to wet the insulation, which then no longer can provide adequate heat flow resistance, and tends to physically degradate. Water present in the materials from which the roof is constructed, or water entering through the top via leaks, or from below as vapor, are typically the sources of the moisture which tends to collect.
In the past, a variety of breather vents have been proposed to alleviate this problem, as exemplified in the following listed patents:
______________________________________ Re.31,549 Ballard et al 4,484,424 Logsdon 3,238,862 Smith et al 4,512,243 Ballard et al 4,184,414 Jarnot 4,593,504 Bonnici et al 4,189,989 Maze 4,622,887 Peterson 4,214,513 Ballard et al 4,706,418 Stewart 4,386,488 Gibbs ______________________________________
With effective stack venting, such wet roofs can be dried over a period of time, and the present vent structure has been conceived to enhance the elimination of moisture from such roof systems.
As noted in an article entitled VENTING OF FLAT ROOFS, by M. C. Baker and C. P. Hedlin, in the "Canadian Building Digest", U.D.C. 69.024.3: 697.92, on page 176-2, "Two transport mechanisms can be in effect in moving moisture through breather vents: the convective moving of air carrying vapor; and vapor diffusion. In addition, wicking along the insulation fibers may help to move moisture laterally through some types of insulation." The article points out that wind can cause a pressure difference which creates convective air movement, as can stack effect, which can be created if some vents are higher than others. On most flat roofs, however, all vent openings will be at approximately the same level, and there will generally be only small pressure differences from wind.
Diffusion, the second transport mechanism involves the movement of water vapor through the insulation to the outside under a vapor pressure difference. The article notes that stack venting is logical for new roofs, as well as wet roofs, and may well take care of small quantities of construction moisture that would otherwise be trapped in the system, as well as small quantities that might get past the vapor barrier. In addition, such vents tend to relieve vapor pressure generated under a heated roof surface.